Superluminescent diode module

ABSTRACT

A module accommodates multiple superluminescent light emitting diodes, SLEDs,  12   r,    12   g  and  12   b . The SLEDs are arranged in an enclosure and output respective light beams to propagate into free space within the enclosure. The individual light beams from the SLED sources are combined into a single beam path within the enclosure using beam combiners  40   r - g,    40   rg - b . Each beam combiner is realized as a planar optical element, the back side of which is arranged to receive a SLED beam and route it through the optical element to the front side where it is combined with another SLED beam that is incident on and reflected by the front side. The free-space propagating combined beam is output from the module via an optical fiber  42  (or through a window).

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims the benefit of andpriority to U.K. Patent Application No. 1820370.3, filed Dec. 13, 2018,which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISC APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to broadband optical source modules.

Background

Superluminescent light emitting diodes (SLEDs) are broadband opticalsources that find application where semiconductor laser diodes areunsuitable, for example because the coherence of laser light cannot betolerated or where a broadband emission spectrum is needed.

For some applications where the light properties of a SLED source are inprinciple suitable, a single SLED cannot be used, since the applicationrequires an emission bandwidth which is broader than a single SLED iscapable of delivering. With current technology, a single SLED is capableof emitting over a bandwidth of, for example, at most 50-70 nm in the800-900 nm wavelength range with sufficient spectral flatness andsufficient output power. In the visible range used for displayapplications, i.e. in the 450-650 nm wavelength range, a single SLED iscapable of emitting over bandwidth of at most 10-30 nm with currenttechnology. Those emission bandwidths are too small for a display orprojector application which requires red (˜640 nm), green (˜520 nm) andblue (˜450 nm), i.e. RGB, emission. The emission bandwidth of a singleSLED is also too small for certain types of optical coherence tomography(OCT) systems.

FIG. 1 is a schematic drawing of a known SLED source system which isbased on using optical fibers with fiber couplers to combine the outputsof two or three SLEDs. The fiber couplers could be fused fiber couplersor fiber-pigtailed free-space filters based on wavelength-divisionmultiplexing (WDM), for example. Modules of this kind have beencommercially available from various companies, for example EXALOS (e.g.,EBS300080-02 with 140 nm FWHM at 845 nm) or Superlum (e.g., M-D-840-HPwith 90-100 nm FWHM at 840 nm).

FIG. 1 shows schematically three SLED source modules in the form ofbutterfly packages with electrical pins 18 (14 pins being illustrated).The three SLED source modules are labelled 5 r, 5 g and 5 brespectively, to indicate that they house respective SLED sources 12,labelled 12 r, 12 g and 12 b for red, green and blue which output lightwith centre wavelengths in the red, green and blue visible wavelengthsas would be the case for a display source. The source modules 5 r/g/beach include an optical fiber pigtail 16 for coupling the light from theSLED source 12 into the end of an optical fiber via a coupling lens 14.The outputs from the upper two SLED modules 5 r, 5 b are carried byrespective optical fibers 20, 22, which lead to a fiber coupler 26 wherethe two outputs 5 r, 5 g are combined into a single output fiber 28. Thelower SLED source module 5 g outputs into an optical fiber 24, whichleads to a fiber coupler 30 where it is connected with the optical fiber28 carrying the outputs from SLED source modules 5 r and 5 g, so thatthe output of the fiber coupler 30 has combined all three source outputsin an optical fiber 32.

The design of FIG. 1 is problematic for applications where a polarizedoutput is needed. It is possible to use polarization-maintaining fiber(PMF). However, this is likely to be difficult to implement, since thepolarization axis of the SLED output needs to be very well matched tothe polarization axis of the PMF if significant losses and unpredictablemode-mixing effects (e.g., polarization crosstalk or polarization modedispersion (PMD)) are to be avoided. Maintaining the polarizationthrough the fiber couplers would also be technically challenging and maynot be possible over large bandwidths, e.g. a few hundred nanometers fora combined beam from three SLEDs of different centre wavelengths.

WO 2006/039154 A1, in FIG. 12 thereof, and US 2005/083533 A1, in FIG. 15thereof, show similar designs of a tunable narrow-band source. Theoutputs from a bank of five SLEDs each pass through a lens, isolator andfurther lens. The individual beams then pass through a bank of fivetunable Fabry-Perot filters, then each through another lens. The beamsare then combined by three mirrors and a beamsplitter and from there fedto an output fiber via two tapping mirrors associated with respective.The disclosed device is a tunable narrow-band source using Fabry-Perotfilters as tuning elements.

US2011/080591 A1, in FIG. 5 thereof, discloses a tunable, externalcavity laser comprising two semiconductor gain sections and, for tuning,an etalon and respective Fabry-Perot filters. The two beam paths fromthe two gain sections are combined by mirror and combiner, with thecombined beam then being fed to a reflection-mode etalon where unwantedbeam components are absorbed. The output is supplied to an optical fiberafter the two beams have been combined by a mirror and a combiner. Thedisclosed device is a tunable narrow-band source using an etalon andFabry-Perot filters as tuning elements.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a modulefor superluminescent light emitting diodes, SLEDs, the modulecomprising: a housing defining an enclosure of free space; a first SLEDsource arranged in the enclosure to emit a first SLED beam having afirst wavelength range to propagate in the free space along a first beampath; a second SLED source arranged in the enclosure to emit a secondSLED beam having a second wavelength range to propagate in the freespace along a second beam path; a beam combiner arranged in theenclosure to receive the first SLED beam and the second SLED beam, andto combine them into a combined SLED beam extending in the free spacealong a combined beam path; and an optical output port arranged toreceive light along the combined beam path and to output the light fromthe housing. The combined SLED beam preferably has a spectrum includingthe first and second wavelength ranges. The spectrum may be a continuousspectrum covering the first and second wavelength ranges.

In some embodiments, the beam combiner is implemented as a substantiallyplanar optical element. The planar optical element has a front side anda back side, the back side being arranged to receive the first SLED beamat a first angle of incidence and route it through the optical elementto the front side and output it from the front side from a firstposition and in a first direction, and the front side being arranged toreceive the second SLED beam at a second position that is coincidentwith the first position and at a second angle of incidence, and toreflect the second SLED beam into a second direction that is coincidentwith the first direction. A first lens component may be arranged in theenclosure to act on the first SLED beam and/or a second lens componentmay be arranged in the enclosure to act on the second SLED beam, e.g.for collimating the SLED output.

A third SLED source may additionally be provided in the module. Thethird SLED source may be arranged in the enclosure to emit a third SLEDbeam having a third wavelength range to propagate in the free spacealong a third beam path. A further beam combiner is then arranged in theenclosure to receive the combined first and second SLED beam and thethird SLED beam, and to combine them into a combined beam path extendingin the free space.

The combined SLED beam preferably has a spectrum including the first,second and third wavelength ranges. The spectrum may be a continuousspectrum covering the first, second and third wavelength ranges. Theoptical output port is arranged to receive light along the combined beampath and to output the light along the combined beam from the housing.The further combiner may be implemented as a substantially planarfurther optical element having a front side and a back side, the backside being arranged to receive the combined first and second SLED beamat a further angle of incidence and route it through the further opticalelement to the front side and output it from the front side from afurther position and in a further direction, and the front side beingarranged to receive the third SLED beam at a third position that iscoincident with the further position and at a third angle of incidence,and to reflect the third SLED beam into a third direction that iscoincident with the further direction. A third lens component may bearranged in the enclosure to act on the third SLED beam.

In embodiments with three or more SLED sources emitting at differentwavelength ranges, these may be arranged in order of ascending ordescending wavelength range.

In embodiments with descending order, the first wavelength range coversa wavelength range that is longer than the second wavelength range,which is longer than the third wavelength range. Here, an edge filtermay be arranged after combining the first SLED beam with the second SLEDbeam and configured to reject wavelength components that are shorterthan the second wavelength range; and a further edge filter arrangedafter combining the previously combined first and second SLED beams withthe third SLED beam and configured to reject wavelength components thatare shorter than the third wavelength range. Moreover, a still furtheredge filter may be arranged in the beam path of the first SLED beambefore it is combined with the second SLED beam and configured to rejectwavelength components that are shorter than the first wavelength range.These edge filters may be incorporated integrally as coatings on theback side of the beam combiners for example.

In embodiments with ascending order, the first wavelength range covers awavelength range that is shorter than the second wavelength range, whichis shorter than the third wavelength range. Here an edge filter may bearranged after combining the first SLED beam with the second SLED beamand configured to reject wavelength components that are longer than thesecond wavelength range; and a further edge filter arranged aftercombining the previously combined first and second SLED beams with thethird SLED beam and configured to reject wavelength components that arelonger than the third wavelength range. Moreover, a still further edgefilter arranged in the beam path of the first SLED beam before it iscombined with the second SLED beam and configured to reject wavelengthcomponents that are longer than the first wavelength range. These edgefilters may be incorporated integrally as coatings on the back side ofthe beam combiners for example.

In some embodiments, one or more beam-shaping components are arranged inthe enclosure. Beam-shaping components may be provided for any one ofthe SLED beams, or all of them, or any other permutation. Thebeam-shaping components may act to transform a collimated SLED beam froman elliptical beam shape into a circular beam shape. Beam-shapingcomponents may also be provided for the combined beam. Moreover, anaperture may be arranged in the combined beam path, e.g. to clean up thecombined beam characteristics and filter out stray light that may bepresent in the enclosure.

The module may further comprise a substrate arranged in the enclosureand having mounted thereon at least the SLED sources and the beamcombiner(s) as well as optionally any other ones of the components asdesired.

As well as SLEDs, the module may accommodate a laser diode, with thelaser diode's beam also being combined into the SLED beams. Namely, themodule may further comprise: a laser diode source arranged in theenclosure to emit a laser beam to propagate in the free space; and afurther beam combiner arranged in the enclosure to combine the laserbeam with at least one of the SLED beams (first, second or combined) topropagate along the combined beam path. Another design alternative is toprovide a module comprising: a housing forming a free-space enclosure;at least a first SLED source arranged in the enclosure to emit a firstSLED beam having a first wavelength range to propagate in the freespace; a laser diode source arranged in the enclosure to emit a laserbeam to propagate in the free space; and a beam combiner arranged in theenclosure to combine the laser beam with at least one of the first SLEDbeam and the second SLED beam into the combined beam path. Withreference to the above discussion of edge filters, when the moduleincludes a laser diode, the laser diode may be arranged in the cascadeof ascending or descending wavelength at the appropriate position andwith an associated edge filter.

In some embodiments, the optical output port comprises: an optical fibercoupler which is attached to an optical fiber and arranged to couple thecombined beam (SLED only or SLED and LD) into an end of an optical fiberto allow the combined beam to output from the housing via the opticalfiber. In other embodiments, the optical output port comprises: a windowarranged in the housing to allow the combined beam (SLED only or SLEDand LD) to output from the housing.

Various arrangements of the SLEDs are possible within the enclosure. Theenclosure may for example be substantially rectangular in plan view, asis the case for a butterfly package. The optical output port may bearranged at one end of the enclosure in an end wall of the housing. Inone arrangement, each of the SLED sources is arranged on the same sideof the enclosure so as to emit their beams substantially in the samedirection across the enclosure.

In an other arrangement, one of the SLED sources is arranged on one sideof the enclosure and another of the SLED sources is arranged on theother side of the enclosure so that they emit their beams insubstantially opposed directions across the enclosure. In a stillfurther arrangement, one of the SLED sources is arranged on one side ofthe enclosure and another of the SLED sources is arranged at an end ofthe enclosure opposite the end that accommodates the optical output portso that they emit their beams in substantially orthogonal directionsacross and along the enclosure respectively.

SLED modules embodying the invention are suited to incorporation into anumber of systems, such as the following.

There may be provided an optical coherence tomography system,comprising: a module according to an embodiment of the invention; and abeam splitter arranged to receive light output from the source moduleand to direct one component into a first, sample arm to a sampleposition and another component to a second, reference arm, and torecombine light received back from the first and second arms and directthe recombined light to a detector.

There may be provided a fundus imaging system, comprising: a moduleaccording to an embodiment of the invention; and an optical arrangementconfigured to direct light output from the source module to a sampleposition and collect light received back from the sample position into afundus imaging unit.

There may be provided an endoscopic imaging system, comprising: a moduleaccording to an embodiment of the invention arranged to direct itsoutput beam into a light guide; and an insertion tube adapted forinsertion into a bodily orifice in which is arranged at least a part ofthe light guide, wherein the light guide terminates proximal a distalend of the insertion tube.

Generally, the number of beam combiners that are needed will be onefewer than the number of beams to be combined.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will now be further described, by way of example only,with reference to the accompanying drawings.

FIG. 1 is a schematic drawing of a known SLED source system.

FIG. 2 is a schematic plan view of a SLED source module according to afirst embodiment with an optical fiber output.

FIGS. 3 and 4 are graphs of output power as a function of wavelength fora SLED source module according to the first embodiment.

FIG. 5 is a schematic plan view of a SLED source module according to asecond embodiment with an optical fiber output.

FIG. 6 is a schematic perspective view of a SLED source module accordingto a third embodiment with a free-space output.

FIG. 7 is a schematic perspective view of a SLED source module accordingto a fourth embodiment with an optical fiber output.

FIG. 8 is a schematic plan view of a SLED source module according to afifth embodiment with individual power monitors for each SLED.

FIG. 9 is a schematic plan view of a source module according to a sixthembodiment combining multiple SLEDs and a laser diode (LD).

FIG. 10 is a schematic plan view of a SLED source module according to aseventh embodiment.

FIG. 11 is a schematic diagram of an example optical coherencetomography (OCT) system which comprises a SLED source module embodyingthe invention.

FIG. 12 shows an example direct projection system in a monocle formatwhich comprises an RGB SLED source module embodying the invention.

FIG. 13 shows an example direct projection system in a spectacles formatwhich comprises an RGB SLED source module embodying the invention.

FIG. 14 is a schematic diagram of an example combined OCT and fundusimaging system which comprises two SLED source modules embodying theinvention.

FIG. 15 is a schematic drawing of a medical device system comprising aSLED source module embodying the invention.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation andnot limitation, specific details are set forth in order to provide abetter understanding of the present disclosure. It will be apparent toone skilled in the art that the present disclosure may be practiced inother embodiments that depart from these specific details.

The wavelength range of an individual SLED emitter is defined by avariety of design parameters including its epitaxial semiconductor stackstructure and materials, the dimensions of the ridge in the case of aridge structure, and the properties of the chip's end facets. Thewavelength range may have a value between 3 nm and 160 nm at full widthhalf maximum (FWHM), i.e. 3 dB attenuation level. It is the case that,for comparable designs, the FWHM scales with the square of wavelength,so the maximum possible wavelength range for comparable designsincreases for longer wavelengths. With future developments in technologyit may be possible to broaden the maximum wavelength range at anyparticular center wavelength. The wavelength range covered by anindividual SLED emitter as disclosed herein may have any value between 3nm and 160 nm. With current technology and using the arsenide- andphosphide-based materials system wavelength ranges up to about 160 nmare achievable in SLEDs with center wavelengths in the near infrared(NIR) and infrared (IR). With current technology and using thenitride-based materials system wavelength ranges up to 30 nm areachievable in blue and green SLEDs. For example, the wavelength rangemay have a value of 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60,70, 80, 90, 100, 110, 120, 130, 140 or 150 nm.

To suppress lasing in edge-emitting ridge SLED structures, as is knownin the art, one or more of the following measures can be undertaken:

(i) the ridge may extend such that its optical path intersects with thechip's front (output) facet at a non-normal angle, either by the ridgebeing straight and extending at a non-normal angle to the parallelplanes of the chip's front and back facets, or by having a curvedportion adjacent the front facet;

(ii) absorber materials may be provided adjacent the back facet whichare absorbent over the SLEDs amplification wavelength range;

(iii) the ridge may terminate part way between the front and backfacets, e.g. at a tilt angle so that reflections from the back facet areinhibited from coupling back into the waveguide; and

(iv) the front and/or back facets may be coated with anti-reflectioncoatings.

In the following detailed description, the repeated references to red,green and blue wavelength ranges, are specific labels that make thedescription of the examples convenient to understand. While these colorsare technically significant for display and projection applications, itwill be understood that they may be generalized to mean first, secondand third different emission wavelength bands from first, second andthird SLEDs. Moreover, one or more of these bands need not be in thevisible region, since for example one or more of the bands may be in thenear infrared, or near ultraviolet.

FIG. 2 is a schematic plan view of a SLED source module according to afirst embodiment with an optical fiber output. The SLED module is basedon a butterfly package 5, shown as a 14-pin butterfly package. Thebutterfly package 5 has a plurality of terminal pins 18 via whichelectrical connections may be made to components housed in the package.The butterfly package 5 has a housing 10 that forms an enclosure inwhich the SLEDs are accommodated as well as associated components. Thecomponents are at least for the most part mounted directly or indirectlyon a main board 34, which may also be referred to as a carrier board,substrate, optical breadboard or mounting board. The main board 34 isprovided with a temperature sensor 54 s arranged on the main board tomeasure the temperature of the main board. The main board 34 should havegood thermal conductivity for heat dissipation, and should bemechanically stiff. Suitable materials choices are ceramic, e.g. AlN orAl2O3, a suitable metal, e.g. copper, aluminium or alloys containingeither or both of these metals such as CuW. The upper and/or lowersurface of the main board 34 may be metallized to support solderprocesses for the attachment of the components, in particular forelectrical connections. Metallization may also aid good thermalconnection to cooling elements for maintaining the temperature insidethe enclosure within a specified range. For physical attachment ofcomponents by bonding, e.g. with epoxy resin, the upper and/or lowersurfaces of the main board 34, or selected areas thereof, may bespecified with a minimum surface roughness to provide good adhesion.

The housing 10 and the enclosure it defines by its internal walls aresubstantially rectangular in plan view as illustrated aligned withorthogonal axes x and z respectively across and along the module asillustrated, with y being the axis out of the paper, i.e. the vertical.The SLED module has its optical output port arranged at one end of theenclosure in an end wall of the housing 10. The optical output port inthis embodiment is realized with optical fiber in the form of an opticalfiber ferrule 16, which is attached to an optical fiber 42 that may besingle mode or multimode and may be polarization maintaining (or not) asdesired. The ferrule 16 and fiber 42 form a so-called pigtail and serveto couple the combined beam from the different SLEDs 12 into the end ofthe optical fiber and thus out of the module 5. The fiber ferrule 16 mayalso be attached to the main board 34, or may be secured to the housing10, e.g. to the end wall. It will be appreciated that the module alsohas a lid (not shown) which may be secured removably or non-removably tothe housing by fasteners, such as screws or rivets, and/or adhesivebonding, welding or other fastening or sealing means as desired.

The components include first, second and third SLED sources 12 r, 12 gand 12 b. The SLEDs 12 are arranged in the enclosure to emit respectivefirst, second and third beams having first, second and third wavelengthranges into free space within the enclosure along first, second andthird beam paths. The three wavelength ranges are labelled as ‘r’, ‘g’and ‘b’ to indicate red, green and blue wavelength ranges by way ofexample, and also to provide intuitive labelling. These could howeverequally well be three wavelength ranges in some other part of thevisible, near-UV or near-infrared (NIR). The SLEDs 12 are mounted onrespective submounts 36, labelled 36 r for the red SLED 12 r, 36 g forthe green SLED 12 g, and 36 b for the blue SLED 12 b. The submounts 36are in turn mounted on the main board 34. The materials choices for thesubmounting boards 36 are similar to those as described above for themain board 34. The mode of assembly with populated submounts on a mainboard is referred to as a chip-on-submount (CoS) in the art. The SLEDchips 12 are schematically shown mounted at an angle to their submounts36 and the sides of the rectangular enclosure as would be the case fortilted, single-pass SLEDs in which the ridge waveguide of the SLED istilted as a way of hindering reflections from the chip end facets, inparticular the back facet, coupling back into the ridge waveguide,thereby to suppress lasing action. Typically, the reflectivity of bothchip end facets is kept as low as possible, and the light is amplifiedalong the waveguide on a single pass. The ridge and hence the underlyingwaveguide W may be straight or incorporate a curved portion.Back-reflection may be further suppressed by introducing a passiveabsorber section in the SLED chip. The choice of SLED type is flexible,e.g. double-pass designs with the back facet having a high reflectivitycould be used. The submounts 36 may also have respective temperaturesensors 54 mounted on them, labelled 54 r for the red SLED submount 36r, 54 g for the green SLED submount 36 g, and 54 b for the blue SLEDsubmount 36 b. These temperature sensors allow the temperature local toeach SLED to be monitored. The temperature sensors 54 s, 54 r/g/b mayhave their signals used as control inputs for one or more coolingelements (not shown). For example the mounting board 34 may haveattached to its upper or lower surface a thermoelectric cooler, e.g. aPeltier device. The submounts 36 r/g/b may also have individual coolingelements (not shown) that can be independently controlled via therespective temperature measurements from sensors 54 /r/g/b.

The SLED output beams from the SLEDs 12 r/g/b are collimated byrespective collimating lenses 38 r/g/b. The red SLED 12 r is arranged onone side of the enclosure and the green and blue SLEDs 12 g, 12 b arearranged on the other side of the enclosure so that the red beampropagates initially in the opposite direction to the blue and greenbeams laterally across the enclosure, i.e. in negative-x and positive-xdirections respectively. The red SLED beam after collimation by lens 38r is deflected through 90 degrees from the negative-x direction into thez-direction by a mirror 40 r arranged at 45 degrees to x and z. Thez-travelling red beam is incident on the back face of a beam combiner 40r-g which has the function of combining the red beam with the greenbeam. The beam combiner 40 r-g is a planar optical element which is madeof a suitable glass or crystal material. The beam combiner 40 r-g has afront side and a back side. The red beam is incident on the back side ofthe beam combiner 40 r-g at an angle of incidence which causes the beamto refract into the beam combiner 40 r-g. The back side is preferablycoated with an antireflection coating (ARC) that is effective for thewavelength range, angle of incidence and polarization state of the redbeam. The red beam is then routed through the glass or crystal to thefront side and is once more refracted as it outputs from the front side.The front side of the beam combiner 40 r-g is arranged to receive thegreen beam propagating in the positive-x direction from the collimatinglens 38 g at a position on the front surface that is the same as wherethe red beam passes through the front surface. Moreover, the beamcombiner 40 r-g is configured and arranged so that the green beamreflected from its front surface propagates in the same direction as thered beam output from the front surface, preferably the z-direction asschematically illustrated. The red and green beams thus emerge from thebeam combiner 40 r-g as a combined beam propagating in free space withinthe enclosure in direction z. The beam combiner 40 r-g will usually beplanar, but if desired it could be slightly curved, but stillsubstantially planar, to provide some focusing or defocusing of one ormore of the red and green beams.

The combined red and green beam is then combined with the blue beam in asimilar way using a further beam combiner labelled 40 rg-b. Namely, theblue beam output from the blue SLED 12 b travelling in the positivex-direction is collimated by collimating lens 38 b and is incident onthe front surface of the beam combiner 40 rg-b, and the back surface ofthe beam combiner 40 rg-b receives the combined red-green beam. The red,blue and green beams thus emerge from the beam combiner 40 rg-b as acombined beam propagating in free space within the enclosure along anoptical path in direction z.

The combined beam is focused onto the end face of the optical fiber 42held in the pigtail ferrule 16 by a coupling lens 14. In addition, tomeasure the power of the combined beam, a tapping mirror 50 is arrangedin the combined beam, e.g. between the coupling lens 14 and fibercoupler 16 as illustrated, to tap off a small part of the beam to apower monitor 52, which may be realized as a photodiode, for example.The tapping mirror 50 may for example be a planar piece of clear glass,i.e. glass that is transparent over the combined wavelength range of thethree components of the combined beam, so that a few percent of thecombined beam, e.g. 1-5% of its power, is reflected away into the powermonitor by residual reflection. Alternatively, a tap mirror could beomitted, and the power monitor could face the point where the combinedbeam is focused onto the fiber end and monitor power through monitoringback-scattered light from the fiber end.

Other design options may be incorporated into the module. For example,edge filters may be incorporated to filter each of the beams prior tothem being combined, so as to filter out wavelengths that are outsidethe wavelength range of each SLED. In the case that the beams arecombined in order of decreasing wavelength, with the shortest wavelengthbeing combined last, as is the case of the embodiment of FIG. 2 wherethe combination order is red then green then blue, then each edge filterwill cut-off wavelengths shorter than the intended wavelength range ofeach SLED. For example, in the embodiment of FIG. 2, if the red SLED isintended to output over a range 700-750 nm, then a suitable edge filtermay reject wavelengths less than 700 nm, or some other value close to700 nm, such as 690, 680, 670 nm etc. as desired. Alternatively, if thebeams are combined in order of increasing wavelength, with the longestwavelength being combined last, e.g. a combination order of blue thengreen then red, then each edge filter will cut-off wavelengths longerthan the intended wavelength range of each SLED. Edge filters may beincorporated integrally into the front side of the mirror 40 r and thefront and/or back sides of the beam combiners 40 r-g, 40 rg-b ascoatings. Alternatively, edge filters may be added as separatecomponents and mounted on the main board 34. Band filters could also beused for filtering out unwanted wavelengths in addition to, or insteadof edge filters.

Another design option is to use a polarization filter on the combinedbeam, e.g. prior to or after the coupling lens 14, to increase thepolarization extinction ratio (PER) of the outputted beam. This may beuseful when the module is specified to have a high PER, e.g. at least20-30 dB, whereas the intrinsic PER of one or more of the SLEDs 12 maybe lower, e.g. only 3-10 dB.

It will be understood that references to a combined beam could be takento imply that the different SLEDs are simultaneously emitting. However,this is not necessarily the case. For a display or projectionapplication, red, green and blue beams will generally be emittingsimultaneously (unless the image is exceptionally only red etc.).However, for other applications, the different SLEDs may be drivenselectively and not all be active at the same time. For example, if themodule is intended for a multi-modality system requiring say one groupof one or more SLEDs to emit in the NIR for OCT and another group of oneor more SLEDs to emit in the visible for fundus imaging, then these twogroups would not generally be operated simultaneously, but these twogroups are nevertheless arranged in the module to have a combined beampath, i.e. so that their beams are (or would be) combined when (or if)they are simultaneously emitted.

FIG. 3 is a graph of output power, P, on a logarithmic scale ofarbitrary units, as a function of wavelength, A, in nanometres for anexample SLED source module according to the first embodiment whichprovides a continuous spectrum in the NIR in the range of about 760-950nm. The spectrum of the combined beam is shown with the solid line, andthe spectra from the individual SLEDs with the dashed, dotted andchain-dotted lines.

FIG. 4 is a graph of output power, P, on a linear scale of arbitraryunits, as a function of wavelength, A, in nanometres for the sameresults as shown in FIG. 3. In other words, FIG. 4 is merely a differentpresentation in the y-axis of the same results as shown in FIG. 3.

The redmost SLED (dashed line) has a centre wavelength of ˜790 nm and abandwidth of 45-50 nm, the middle SLED (dotted line) has a centrewavelength of ˜840 nm and a bandwidth of 50-55 nm, and the infraredmostSLED (dashed-dotted line) has a centre wavelength of ˜880 nm and abandwidth of 55-60 nm. The specification of the SLED source module'soutput is: centre wavelength of 845 nm, 3 dB bandwidth of 145 nm, 10 dBbandwidth of 165 nm, 10 dB wavelength range of 765-930 nm, 10 mW outputpower and a coherence length of 2.9 micrometres. It will be appreciatedthis output is from the red end of the visible to near-infrared, whichis suitable for OCT systems. With other SLED sources currentlyavailable, other wavelength ranges can be covered, e.g. spanning thevisible range, such as needed for RGB displays, and ranges further intothe near-infrared. It is expected that improved specifications willbecome available with the present designs as SLED sources continue toimprove their performance.

FIG. 5 is a schematic plan view of a SLED source module according to asecond embodiment with an optical fiber output. The embodiment of FIG. 5only differs from that of FIG. 2 in that the mirror 40 r of FIG. 2 isomitted, since the red SLED source 12 r is arranged to emit along theenclosure in the z-direction and directly project onto the back face ofthe beam combiner 40 r-g via the collimating lens 38 r.

FIG. 6 is a schematic perspective view of a SLED source module accordingto a third embodiment with a free-space output. The optical output portcomprises a window 48 arranged in the end wall of the housing 10 toallow the combined beam to be output from the housing in thez-direction. Compared with FIGS. 2 and 5 with optical fiber output,there is no requirement for a focusing lens 14 in the embodiment of FIG.6, so this is omitted from the drawing. However, optionally, a lens inthe same position as lens 14 of FIGS. 2 and 5 could be included in theembodiment of FIG. 6, but this need not be for creating a focus withinthe enclosure, but rather more likely would be provided to bring theoutput light beam to a defined focus some specified distance away fromthe module, or for providing an auxiliary or supplementary collimatingfunction for the combined beam additional to that provided by theindividual collimating lenses 38. Also visible in FIG. 6 are the endflanges 56 of the butterfly package 5, which are also present in theembodiments of FIGS. 2 and 5, although not illustrated. Moreover,compared with FIG. 2 and also FIG. 5, it can be seen that in FIG. 6 allthree SLED sources 12 on their respective boards 36 are arranged on thesame side of the enclosure all emitting in the same direction across theenclosure, so that compared with FIG. 2 mirror 40 r is aligned withsimilar rotation to the planar beam combiners 40 r-g and 40 rg-b. Thisarrangement results in the combined first, second and third output beamsbeing closer to the sidewall of the housing 10, so that two beam offsetmirrors 44, 46 are provided for bringing the combined output beam awayfrom the sidewall and back to a more central position aligned with thecentre of the output window. The power monitor 52 is arranged to receivea small power component, e.g. 1-3%, of the combined output beam that istransmitted through the first beam offset mirror 44, i.e. is arranged‘behind’ the beam offset mirror 44. For this purpose, the first beamoffset mirror 44 may be designed with a reflectivity to the combinedbeam of slightly less than 100%. The power monitor 52 could instead bearranged behind the second beam offset mirror 46. The beam offsetmirrors 44, 46 are attached to the mounting board 34. The beam offsetmirrors 44, 46 will in the normal case be planar, but they could be madeconcave or convex if desired to provide some focusing, collimating ordefocusing effect. It will be appreciated that this arrangement with allthe SLED sources 12 arranged on the same side of the enclosure is alsoavailable with optical fiber output, i.e. in conjunction with a fiberferrule 16 and optical fiber 42 as shown in FIGS. 2 and 5.

FIG. 7 is a schematic perspective view of a SLED source module accordingto a fourth embodiment with visible, RGB-SLEDs and an optical fiberoutput. The design corresponds to that of FIG. 6, except that instead ofa window 48, there is an optical fiber ferrule 16 and optical fiber 42forming a pigtail arrangement, as in the embodiments of FIG. 2 and FIG.5 with the power monitor 52 facing the fiber end where the combined SLEDbeams are focused by coupling lens 14.

In the above embodiments, attachment of the components to the main board34, the submounts 36 and the housing 10 may be by UV-curable epoxyresin. The attachment is done with high accuracy placement. Activealignment, i.e. with the SLED sources switched on during alignment, maybe used during the component attachment to ensure that the differentoptical components are correctly located for guiding and combining thedifferent beams as desired. Active alignment may also help ensureefficient coupling into an output fiber or that a free-space beam hasthe desired output direction, position and focal properties (e.g. isprecisely collimated or with a focus at a specified distance from themodule). After UV-curing of the epoxy resin, the main board 34 with itsattached components may be baked in an oven. It will be appreciated thecomponents 14, 38, 40 etc. may not be single components as illustrated,but may each consist of two or more components, such as isolators(electrical, thermal and/or vibration), and submounts. Moreover,physically separate filters, polarizers, apertures or other opticalcomponents (not illustrated) may also be included that are attached tothe mounting board 34.

FIG. 8 is a schematic plan view of a SLED source module according to afifth embodiment. The design of FIG. 8 is similar to that of FIG. 6, butdiffers in that individual power monitors 52 r/g/b are provided for eachof the SLEDs 12 r/g/b respectively (instead of having one power monitor52 for the combined RGB beam). Each individual power monitor 52 isarranged to receive a small fraction of the light power that has beentransmitted through the deflecting mirror or beam combiner 40, thesebeing configured to have slightly less than 100% reflection to the SLEDbeam, so that a small power fraction, e.g. 1-3%, of the SLED beam passesthrough the element 40 to the power monitor 52. Other options forarranging the power monitors are possible. For example, the individualpower monitors could be arranged adjacent the back facet of each SLED inorder to measure the light that ‘leaks’, i.e. is emitted, from the backfacet of the SLED. Having power monitors for each SLED may be useful ina number of applications. For example, it may be useful when the outputneeds to meet particular safety standards, and those safety standardsspecify different safety limits for different ones of the wavelengthranges output by the SLEDs. The outputs from the power monitors wouldthen be supplied to a controller that would control the drive currentsof each SLED so that the output power from each SLED did not exceed anupper limit. For example, in laser class 1, the safety limit for bluelight is approximately an order of magnitude lower than for green andred light. Having individual power monitors for each SLED may also bebeneficial in projector or display applications where true color isimportant, since these can be used to maintain the correct color balancevia feedback to a controller which controls the SLED drive currentsaccordingly. Having individual power monitors for each SLED may beparticularly beneficial when the package is not under tightenvironmental control, e.g. when the package has no or limitedtemperature control features, such as temperature sensors (thermometers)and cooling devices. A further level of sophistication would be wherethe power monitors are adapted to detect also spectral information, i.e.power as a function of wavelength. For example, a dual-photodiodedetector could be employed as the element 52, where the two photodiodeshave different spectral response curves (e.g., by means of a spectralfilter placed on top of the photosensitive area) to allow monitoringpower changes on a wavelength-dependent basis.

FIG. 9 is a schematic plan view of a source module according to a sixthembodiment combining multiple SLEDs and a laser diode, i.e. a combinedSLED and LD module. The design of FIG. 9 may be considered to combinethe three SLEDs and associated components of the design of FIG. 8 with alaser diode source 121 which is arranged in an analogous position to thered emitter of FIG. 5 to emit along the enclosure in the z-direction anddirectly project onto the back face of a beam combiner 401 r-g via acollimating lens 381. In this way, the laser beam output from the laserdiode 121 is combined and collinearly aligned with the combined SLEDoutput beam to form a single output beam path, i.e. an output with acommon optical axis. The laser diode 121 may be an edge emitting laser,or a vertical cavity surface emitting laser. As an aside, it is notedthat the illustrated module has free-space output via a window 48, but avariant with fiber output as in FIG. 8 is also possible. Practical usesof a module according to this embodiment may include use as a source foran ophthalmic instrument. An embodiment may include two or three SLEDsarranged to provide a common output as a combined beam for one modality,as well as a laser diode for another modality. For example, there couldbe a group of three RGB SLEDs for color fundus imaging as well as alaser diode with an output at 488 nm for dye excitation in fluorescenceimaging, or spectroscopy, all accommodated in the same package. Anotheruseful application may be a module with a plurality of SLEDs to providea combined beam for OCT in combination with a laser diode for surgery,e.g. micro-vascular surgery in the retina. OCT measurements could thusbe integrated with the surgical intervention. Further variants of thisembodiment would be to accommodate a second or still further laserdiodes in addition to the plurality of two or more SLED sources, oranother group of SLEDs, e.g. to have an NIR group and an RGB group. Themodule may thus include SLED sources, or a mixture of SLED and LDsources, that are associated with different modalities. Each modalitymay require a single SLED or laser diode source, or a group of two ormore SLED or laser diode sources. Modules according to embodiments ofthe invention may thus provide a single package for multi-modalityapplications, e.g. two, three, four or more different modalities.

FIG. 10 is a schematic plan view of a source module according to aseventh embodiment which, compared with previous embodiments,additionally incorporates beam-shaping components and a diaphragm. Theoutput coupling is free-space output through a window 48 in the end wallof the housing 10, but it will be understood that a variant with fiberoutput is also possible. The other components and their generalarrangement will be recognized from the previous embodiments, namely abutterfly package 5 with pins 18 accommodates first, second and thirdSLED sources 12 r, 12 g and 12 b, labelled ‘r’, ‘g’ and ‘b’. As in theprevious embodiments, the SLEDs 12 r/g/b are mounted on respectivesubmounts 36 r/g/b, which are mounted on a main board 34. The SLEDs 12r/g/b have respective temperature sensors 54 r/g/b arranged proximalthereto on the submounts 36 r/g/b as well as a further temperaturesensor 54 s being provided on the main board 34. Collimating lenses 38r/g/b are arranged to collimate the divergent output beams from theSLEDs 12 r/g/b. The SLED sources 12 r/g/b and their collimating lenses38 r/g/b are arranged on one side of the enclosure so as to generatecollimated beams propagating across the enclosure in the x-direction. Asin previous embodiments, a mirror 40 r is provided for directing thecollimated red beam into the z-direction as well as beam combiners 40r-g and 40 rg-b for directing the collimated green and blue beams intothe z-direction and combining them with the red beam and thered-and-green beam respectively.

However, in contrast to previous embodiments, additional beam-shapingprism components 60 r/g/b are arranged in the respective beam pathsbetween the collimating lenses 38 r/g/b and the mirror and combinerelements 40 r, 40 r-g and 40 rg-b. Beam shaping may be important forSLED sources, since SLED sources tend to have a pronounced beamellipticity due to their specific design rules (e.g., having arelatively high optical confinement in the waveguide to improveelectro-optical efficiency, therefore resulting in relatively largevertical far field angles). A beam-shaping prism as provided here actsto transform an elliptical beam into a circular beam by magnifying theelliptical beam in one dimension. The beam-shaping prism for each of theindividual SLED beams is schematically illustrated as a singleanamorphic prism. As a consequence, the beam is deflected out of thex-direction, so the the mirror and combiner elements 40 r, 40 r-g and 40rg-b are tilted away from a 45 degree orientation in order that theydeflect the beams into the z-direction. However, an anamorphic prismpair could be used instead of a single anamorphic prism in which casethe mirror and combiner elements 40 r, 40 r-g and 40 rg-b could bearranged at 45 degrees as in the previous embodiments. The reason whybeam-shaping prisms 60 r/g/b may be useful is that, after thecollimation lenses 38 r/g/b, the individual beams of the SLEDs may nothave the same beam diameter in the horizontal and/or vertical directions(respectively z- and y-directions in the drawings). This is because thelight from different SLED sources will not in general be emitted withthe same divergence angles; in particular the divergence angle(far-field angles) for the horizontal (slow) axis and vertical (fast)axis are usually quite different, therefore resulting in a larger beamdiameter in the vertical direction and a smaller beam diameter in thehorizontal direction. Beam-shaping may be needed for certainapplications, such as projector or display applications, in order tomeet a specification requirement to have the same beam diameters andhence the same divergence angles in both horizontal and verticaldirection for all three colors of the color palette, i.e. RGB here foradditive mixing, or cyan, magenta and yellow (CMY) for negative mixing.

After the beams have been combined and before the combined beam isoutput from the module, the combined output beam is fed through ananamorphic prism pair 60 w 1, 60 w 2 to provide further beam shaping.With an anamorphic prism pair, it is noted that the prisms can bearranged relative to each other so that the input and output beams areparallel, i.e. have the same propagation direction, but offset from eachother. The beam-shaping prisms for the white (combined) beam could alsobe useful for performing a final adjustment to the ellipticity of thecombined beam as might be desirable for display or projectorapplications, or for imaging applications where a certain beam shape onthe object/sample is needed, as is the case for fundus imaging, forexample.

An aperture 62 (diaphragm/iris) is arranged prior to the output to cleanup the output beam characteristics, for example to remove diffractionartefacts that may have arisen as a result of the collimation lenses orother unwanted effects. The aperture 62 may also serve to block anystray light that is present within the enclosure of the optical modulefrom exiting the optical module. The diameter of the aperture maytypically be between about 0.25 mm and 2 mm, for example 0.30 mm, 0.50mm, 0.75 mm, 1.00 mm, 1.25 mm, 1.50 mm. The aperture could be integratedinto the optical window 48 of the module. Further apertures may beprovided for other beams, such as for the red, green or blue SLED beams,or for the combined red and green beam. It will be understood thatprovision of apertures is an independent design choice not linked toprovision of beam-shaping optics, so for example any of the previousembodiments could be modified by providing apertures and/or beam-shapingprisms.

It will also be understood that beam-shaping prisms may be providedselectively as needed, e.g. beam shaping may only be needed for one ortwo of the SLEDs. A beam-shaping prism or prism pair may also beprovided for shaping the output beam of a laser diode in the case thatthe module also includes a laser diode. Beam clean-up using beam-shapingprisms and/or apertures (diaphragms/irises) may be particularly usefulwhen the module is of the type with a free-space output to improve thequality of the output beam, but may also be useful for optical fiberoutput to improve coupling efficiency into the fiber.

In any of the above embodiments, the beam combiners which receive alight beam on their back faces preferably have antireflection coatings(ARCs) on their back faces. Each ARC will typically be optimized for theincident wavelength range, the incident angle and the incidentpolarization state of the incident beam. The beam combiners mayadditionally or instead have integrally formed on their back faces,and/or their front faces, coatings for other purposes such aswavelength-dependent filtering, e.g. an edge filter, and polarization,e.g. linear polarizer.

It will be understood that variants of any of the above embodiments maybe realized which exchange the red, green and blue SLEDs with SLEDs inother wavelength ranges that can be fabricated with availablesemiconductor crystal materials. In the above embodiments, the SLEDs maybe based on edge-emitting ridge structures. The principal materialssystems of choice are GaAlInN (sometimes referred to as GaN-based ornitride-based), GaAlInP (sometimes referred to as phosphide-based) andGaAlAs (sometimes referred to as arsenide-based). Such modules could bealso realized with SLED devices based on the InP material systems forbroadband light sources in the wavelength range of 1200 to 1900 nm, forexample. For current commercial SLEDs in the visible and near infrared(NIR) ranges, phosphide- and arsenide-based systems are predominantlyused for red wavelengths and nitride-based systems for blue and greenwavelengths. The wavelength range of each SLED may be, for example,between 3 nm and 30 nm at full width half maximum, i.e. at 3 dBattenuation, in the visible range or between 10 nm and 160 nm in the NIRrange.

In the above embodiments, the beam combiners could have any of thefollowing features. The beam combiners could have polarising beamsplitter properties in that they behave in a way that depends on thepolarization state of the incident light to reflect one polarization(e.g. TE/horizontal) and transmit another (e.g. TM/vertical) or viceversa. The beam combiners may reflect or transmit depending on whetherthe incident light is above or below a threshold wavelength, such asreflecting shorter wavelengths and transmitting longer wavelengths orvice versa in the manner of a combiner used for wavelength divisionmultiplexing applications. The beam combiners may also be provided withdifferent splitting ratios as desired, e.g. for power balancing and totap off a portion of the power for power monitoring.

It will be understood that the 3-SLED source embodiments described abovecan be modified to remove one of the SLEDs to provide corresponding2-SLED source modules. For example, in the case of the embodiment ofFIG. 5, if the “blue” SLED components were removed to make a 2-SLEDmodule, then only one mirror would remain, namely mirror 40 g.

While the illustrated embodiments have 3 SLED sources, furtherembodiments may be implemented with four, five, six or more SLEDs. TheSLEDs are preferably arranged on a common substrate 34. The SLEDs areintegrated in a common package as described in the above embodiments for3 SLEDs. With higher numbers of SLEDs, larger packages may be needed,e.g. butterfly packages with more than 18 pins that have more internalvolume. Four or more SLEDs may be beneficial for achieving a desiredspecification, for example to span a wider spectrum than would bepossible with three SLEDs, or to combine visible (e.g., RGB) SLEDemitters with NIR SLED emitters or LDs to support multiple modes of use(modalities) in a single module. One concrete example, would be to havean optical module accommodating one group of, e.g. 2 or 3, SLEDs for RGBoutput (e.g., for color fundus imaging) and another group of, e.g. 3,SLEDs for high-resolution (HR) OCT. Another concrete example would be amodule with a combined SLED source (e.g. with 3 SLEDs) for HR-OCT in thewavelength range 780-930 nm and a further single SLED source with acenter wavelength of around 750 nm for scanning laser ophthalmoscopy(SLO) and/or eye tracking.

Some system applications employing modules as described above are nowdiscussed.

FIG. 11 is a schematic drawing of a static-field Fourier-domain OCTsystem employing a SLED source module as described above to provideillumination over an area of the sample. This is a spectral domainsystem using the broad-band, high-brightness SLED source module and adetector to separate the wavelengths spatially and project them onto aone- or two-dimensional (2d), i.e. array, sensor. The illustrated partsare as follows:

SLED SLED source module A1 aperture BS beam splitter L0-L7 achromaticlenses NDF neutral density filter M1-M4 mirrors DP dispersion prism GRdiffraction grating DU detector unit DA detector array

The SLED source module SLED outputs a circular section beam which passesthrough circular aperture A1, is reflected 90 degrees by a plane mirrorM1 and is then focused by spherical lens L1. A beam splitter BS isarranged to split the light into a first component and a secondcomponent. The first component traverses a sample arm by being projectedonto a mirror M4. The light is reflected by 90° from the mirror M4. Thebeam is collimated by lens L6, projected onto mirror M3 and once againfocused using lens L7. A human eye is placed with its lens being in anappropriate position, e.g. at the focal position of lens L2 asillustrated. The light which is backscattered from the retina isdirected back through the same path until beam splitter BS. At the beamsplitter BS the backscattered component interferes with the secondcomponent returning from the reference arm. Meanwhile, in the referencearm, the source light after passing for the first time through the beamsplitter BS passes through a neutral density filter NDF to adjust thepower; after that it is recollimated by cylindrical lens L2 andreflected by 90° using mirror M2. It further passes a dispersion prismDP to compensate for the dispersion in the sample arm. It is reflectedby 180° with mirror M5. The reflected beam then goes back through thesame path in the reference arm until it reaches the beam splitter BS,where it interferes with the backscattered component from the samplearm. From the beam splitter BS the combined components from the sampleand reference arms are projected via lenses L3 and L4 into the detectorunit DU. A diffraction grating GR which spatially separates thewavelength components and projects them onto a 2D sensor DA via acollimating lens L5, this 2D setup being suitable in a spectral domainconfiguration using a broadband source. It will be understood that theillustrated transmission diffraction grating GR could be replaced by areflection diffraction grating.

It will be understood by those skilled in the art of OCT systems, that afree-space beam splitter BS as illustrated may be substituted with afused fiber coupler, and the free-space beam paths between the opticalelements with optical fiber, in particular single-mode optical fiber, sothat the interferometric part of the OCT system, i.e. the four armsaround the beam splitter, is implemented in optical fiber and opticalfiber components.

We have illustrated a specific static OCT configuration, by way ofexample only, but the SLED source module is also suitable for otherkinds of OCT system. Example OCT systems that may use a SLED sourcemodule as described above include: imaging and sensing techniques, wherethe beam is kept static; imaging and sensing techniques, where the beamis scanned across an object; illumination, where the beam is keptstatic; and illumination, where the beam is scanned. Scanning devicesare, in the context of this disclosure, understood to include methodsthat move a beam across an object. The beam might also be spatiallymodulated, e.g. by using digital mirror devices, spatial lightmodulators or similar.

FIG. 12 shows an example direct projection system in a monocle format,i.e. glasses or spectacles for a single eye. A housing 37 is integratedmidway along a temple 40 and houses an RGB SLED module 45 as describedabove. The combined RGB light beam 35 output by the SLED module 45 isdirected to a scanning element 36 which projects an image on the insidesurface of a lens 42 which is then reflected onto a wearer's eye E todirectly project into the eye. It will be understood that the same basicstructure would be suitable for conventional use, where an image isformed on the inside surface of the lens for the wearer to viewconventionally. Moreover, it will be understood that the reference tothe lens 42 does not imply that the lens 42 has any lensing functioninsofar as the projection system is concerned, rather it merely servesto provide a reflection surface for direct projection (or projectionsurface for conventional projection).

FIG. 13 shows an example direct projection system in a spectacles formatwhich is essentially a doubled-up version of the single-eye system ofFIG. 12 for direct projection into the left eye EL and right eye ER. Thesame reference numerals are used. Projection into both eyes allows foradditional possibilities, such as stereoscopic imaging for 3D.

FIG. 14 is a schematic drawing of a combined OCT and fundus imagingsystem for obtaining images of a human or mammalian eye employing twoSLED source modules as described above, one with IR output band for OCTimaging and another with a visible (RGB) output band for fundus imaging.The specification of the RGB SLED source module is, for example: a blueSLED with a center wavelength of 455 nm and a 3-dB bandwidth of 10 nm, agreen SLED with a center wavelength of 510 nm and a 3-dB bandwidth of 10nm, and a red SLED with a center wavelength of 650 nm and a 3-dBbandwidth of 10 nm. The specification of the IR output may be met by asingle IR SLED, for example a SLED with a center wavelength of 845 nm, 3dB bandwidth of 145 nm, 10 dB bandwidth of 165 nm, 10 dB wavelengthrange of 765-930 nm, 10 mW output power and a coherence length of 2.9micrometers. It will be appreciated this output is from the red end ofthe visible to near-infrared, which is suitable for OCT systems. Theparts shown are as follows:

SLED (IR) IR SLED source module SLED (RGB) RGB/white-light source moduleBS1, BS2 beam splitters L1 lens M1, M2, M3 mirrors

Each SLED module outputs a collimated, circular or elliptical sectionbeam. The collimated beams are reflected 90 degrees by plane mirrors M1and M2 into a common path, wherein mirror M2 allows the IR SLED beam topass through it and combine with the RGB SLED beam at the front face ofmirror M2. A beam splitter BS1 is arranged to reflect the IR and SLEDbeam into a path, called the sample arm, that features a focusing lensL1, which focuses the SLED beams onto a desired focal plane on the eye,e.g. cornea, lens, pupil or retina. A certain portion of the IR/RGBlight is transmitted at beam splitter BS1 into a separated path, calledthe reference arm, which incorporates another mirror M3 that reflectsthe IR/RGB light and that has a path length that is matched to the pathlength of the sample arm. The light which is backscattered from the eyeis directed back through the same path until beam splitter BS1, wherethe IR light of both sample and reference arm interfere. At the beamsplitter BS1 the backscattered component passes through withoutreflection to a second beam splitter BS2 which allows the IR componentof the light to pass through it and be received by an OCT imaging unitand which reflects the RGB component of the light by 90 degrees into afundus imaging unit. We have illustrated a specific static-fieldOCT/fundus imaging configuration, by way of example only, but the SLEDsource module is also suitable for use in a scanning field OCT/fundussystem. Example applications of the IR SLED source module include:spectral-domain or Fourier-domain OCT where the beam is focused to asmall point of high lateral resolution and scanned in two dimensionsacross an object; spectral-domain or Fourier-domain line-field OCTimaging where the beam is focused to a narrow line and scanned in onedimension across an object; spectral-domain or Fourier-domain full-fieldOCT imaging where the beam is kept static and not scanned across anobject; spectral-domain or Fourier-domain optical coherence microscopy(OCM) where the beam is focused to a small point or narrow line andscanned across an object. The beam might also be spatially modulated,e.g., by using digital mirror devices, spatial light modulators orsimilar. It will be understood that either the OCT-specific or thefundus-specific components could be removed from the illustrated systemto make a fundus system or an OCT system respectively.

FIG. 15 is a schematic drawing of a medical device system comprising aSLED module 100 as described above and downstream optical componentsthat form an endoscopic, laparoscopic, bronchoscopic or catheter-likemedical device. An optical path 250 connects the source module 100 andan optical circulator 400. The system further comprises an insertiontube 470, which may be rigid or flexible, suitable for insertion into apatient, for example into a bodily orifice, such as a blood vessel,digestive tract, lung, colon, esophagus etc. The insertion tube 470includes a light guide 480 which may be formed entirely or in part froman optical fiber or optical fiber bundle, or may be a hollow lightguiding tube or some other light guide, and may include free-spaceoptical elements such as lenses, e.g. for collimating, coupling in,coupling out and focusing. The light guide terminates at or near adistal tip 490 of the insertion tube. Light from the source module 100is supplied to the distal tip 490 via the circulator 400 and anynecessary coupling optics (not shown) between the circulator 400 andproximal end 500 of the insertion tube. Light collected from the samplearea adjacent the distal tip 490 of the insertion tube 470, e.g. byscattering or fluorescence, may be guided back to the detection opticsalso by the same light guide 480 that conveyed the excitation light, orvia a different light guide (not shown) arranged in the insertion tube470. The collected light passes through the circulator 400 via a lightpath 510 to a spectrometer 520 and light detector 530. If no spectralfiltering of the collected light signal is needed, then a spectrometerwill of course not be present prior to the light detector. The lightdetector 530 may be an array detector such as a charged coupled device(CCD) or photodiode array, or a light detector without spatialresolution, e.g. a single photodiode. The system is under the control ofa controller 350 via control lines schematically illustrated withdouble-headed arrows which may additionally have data processingfunctionality, e.g. for image processing or other data analysis ofsignals received at the detector 530. Alternatively, measurement datamay be passed, e.g. by the controller, to a separate computing apparatusfor image processing and/or data analysis. Another variation would be toreplace the circulator with a fused fiber coupler or free-space coupler.As well as a plurality of SLEDs, the source module 100 may also includea laser diode as in the embodiment of FIG. 9 which can be used forsurgical purposes, such as polyp removal.

It will be clear to one skilled in the art that many improvements andmodifications can be made to the foregoing exemplary embodiments withoutdeparting from the scope of the present disclosure.

What is claimed is:
 1. An optical coherence tomography or microscopysystem, comprising: a broadband optical source module; and aninterferometric part, wherein the broadband optical source modulecomprises: a housing defining an enclosure of free space; a firstsuperluminescent light emitting diode, SLED, source arranged in theenclosure to emit a first SLED beam having a first wavelength range ofbetween 3 nm and 160 nm at full width half maximum and a first centrewavelength to propagate in the free space along a first beam path; asecond SLED source arranged in the enclosure to emit a second SLED beamhaving a second wavelength range of between 3 nm and 160 nm at fullwidth half maximum and a second centre wavelength different from thefirst centre wavelength to propagate in the free space along a secondbeam path; a beam combiner arranged in the enclosure to receive thefirst SLED beam and the second SLED beam, and to combine them into acombined SLED beam with a continuous spectrum covering the first andsecond wavelength ranges and extending in the free space along acombined beam path; an edge or bandpass filter arranged prior to orafter combining the first SLED beam with the second SLED beam, orincorporated integrally into the front and/or back sides of the beamcombiner as coatings, and configured to reject wavelength componentsthat are shorter or longer than the second wavelength range; and anoptical output port arranged to receive light along the combined beampath and to output the combined SLED beam with the continuous spectrumfrom the housing.
 2. The system of claim 1, wherein the beam combinercomprises a substantially planar optical element having a front side anda back side, the back side being arranged to receive the first SLED beamat a first angle of incidence and route it through the optical elementto the front side and output it from the front side from a firstposition and in a first direction, and the front side being arranged toreceive the second SLED beam at a second position that is coincidentwith the first position and at a second angle of incidence, and toreflect the second SLED beam into a second direction that is coincidentwith the first direction.
 3. The system of claim 1, further comprising:a first lens component arranged in the enclosure to act on the firstSLED beam.
 4. The system of claim 1, further comprising: a second lenscomponent arranged in the enclosure to act on the second SLED beam. 5.The system of claim 1, further comprising: a third SLED source arrangedin the enclosure to emit a third SLED beam having a third wavelengthrange of between 3 nm and 160 nm at full width half maximum and a thirdcentre wavelength different from the first and second centre wavelengthsto propagate in the free space along a third beam path; and a furtherbeam combiner arranged in the enclosure to receive the combined firstand second SLED beam and the third SLED beam, and to combine them toform a combined SLED beam with a continuous spectrum covering the first,second and third wavelength ranges into the combined beam path.
 6. Thesystem of claim 5, wherein the further combiner comprises asubstantially planar further optical element having a front side and aback side, the back side being arranged to receive the combined firstand second SLED beam at a further angle of incidence and route itthrough the further optical element to the front side and output it fromthe front side from a further position and in a further direction, andthe front side being arranged to receive the third SLED beam at a thirdposition that is coincident with the further position and at a thirdangle of incidence, and to reflect the third SLED beam into a thirddirection that is coincident with the further direction.
 7. The systemof claim 6, further comprising: a third lens component arranged in theenclosure to act on the third SLED beam.
 8. The system of claim 5,wherein the first wavelength range covers a wavelength range that islonger than the second wavelength range, which is longer than the thirdwavelength range.
 9. The system of claim 8 wherein the edge or bandpassfilter is configured to reject wavelength components that are shorterthan the second wavelength range; and a further edge or bandpass filterarranged after combining the previously combined first and second SLEDbeams with the third SLED beam and configured to reject wavelengthcomponents that are shorter than the third wavelength range.
 10. Thesystem of claim 9 comprising: a still further edge or bandpass filterarranged in the beam path of the first SLED beam before it is combinedwith the second SLED beam and configured to reject wavelength componentsthat are shorter than the first wavelength range.
 11. The system ofclaim 5, wherein the first wavelength range covers a wavelength rangethat is shorter than the second wavelength range, which is shorter thanthe third wavelength range.
 12. The system of claim 11 wherein the edgeor bandpass filter is configured to reject wavelength components thatare longer than the second wavelength range; and a further edge orbandpass filter is arranged after combining the previously combinedfirst and second SLED beams with the third SLED beam and configured toreject wavelength components that are longer than the third wavelengthrange.
 13. The system of claim 12 comprising: a still further edge orbandpass filter arranged in the beam path of the first SLED beam beforeit is combined with the second SLED beam and configured to rejectwavelength components that are longer than the first wavelength range.14. The system of claim 5, further comprising: a first beam-shapingcomponent arranged in the enclosure in the first beam path to act on thefirst SLED beam; a second beam-shaping component arranged in theenclosure in the second beam path to act on the second SLED beam; and athird beam-shaping component arranged in the enclosure in the third beampath to act on the third SLED beam.
 15. The system of claim 5, furthercomprising a third beam-shaping component arranged in the enclosure inthe third beam path to act on the third SLED beam.
 16. The system ofclaim 1, further comprising: a substrate arranged in the enclosure andhaving mounted thereon at least the SLED sources and the beam combiner.17. The system of claim 1, further comprising: a laser diode sourcearranged in the enclosure to emit a laser beam to propagate in the freespace; and a further beam combiner arranged in the enclosure so that thelaser beam and the SLED beams are combined to propagate along thecombined beam path.
 18. The system of claim 1, wherein the opticaloutput port comprises: a window arranged in the housing to allow thecombined SLED beam to output from the housing.
 19. The system of claim1, wherein the enclosure is substantially rectangular in plan view andthe optical output port is arranged at one end of the enclosure in anend wall of the housing.
 20. The system of claim 19, wherein each of theSLED sources is arranged on one side of the enclosure so as to emittheir beams substantially in the same direction across the enclosure.21. The system of claim 19, wherein at least one of the SLED sources isarranged on one side of the enclosure and at least one other of the SLEDsources is arranged on the other side of the enclosure so that they emittheir beams in substantially opposed directions across the enclosure.22. The system of claim 19, wherein at least one of the SLED sources isarranged on one side of the enclosure and at least one other of the SLEDsources is arranged at an end of the enclosure opposite the end thataccommodates the optical output port so that they emit their beams insubstantially orthogonal directions across and along the enclosurerespectively.
 23. The system of claim 1, wherein the interferometricpart of the system comprises a beam splitter and recombiner arranged toreceive light output from the source module and to direct one componentinto a first, sample arm to a sample position and another component to asecond, reference arm, and to recombine light received back from thefirst and second arms and direct the recombined light to a detector. 24.The system of claim 1, further comprising a first beam-shaping componentarranged in the enclosure in the first beam path to act on the firstSLED beam.
 25. The system of claim 24, further comprising: a secondbeam-shaping component arranged in the enclosure in the second beam pathto act on the second SLED beam.
 26. The system of claim 1, furthercomprising a second beam-shaping component arranged in the enclosure inthe second beam path to act on the second SLED beam.
 27. The system ofclaim 1, further comprising a further beam-shaping component arranged inthe enclosure in the combined beam path.
 28. The system of claim 1,wherein the optical output port comprises: an optical fiber couplerwhich is attached to an optical fiber and arranged to couple thecombined SLED beam into an end of an optical fiber to allow the combinedSLED beam to output from the housing via the optical fiber.